1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to a method and apparatus for controlling uplink transmit power control with optimum delay.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). For example, China is pursuing TD-SCDMA as the underlying air interface in the UTRAN architecture with its existing GSM infrastructure as the core network. The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks. HSPA is a collection of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing wideband protocols.
Generally, uplink (also referred to as “UL”) transmit power control in a mobile communication system balances the need for sufficient energy transmitted per bit to achieve a desired quality of service (e.g., data rate and error rate), against the need to minimize interference to other users of the system and to maximize the battery life of a user equipment (UE). To accomplish this goal, uplink transmit power control has to account for characteristics of a radio propagation channel, including path loss, shadowing, fast fading and interference from other users in the same cell and adjacent cells.
In a TD-SCDMA system, uplink transmit power of a UE is typically controlled by uplink transmit power control commands (e.g., Transmit Power Control (TPC) commands or TPC_cmds) that are sent from a base station (e.g., a Node B in UMTS) to the UE through a downlink (also referred to as “DL”) channel. For example, a Node B attempts to maintain a signal-to-interference (SIR) target for received signals from the UE, and sends transmit power control commands to the UE based on how an estimated SIR of a received signal compares to the SIR target. The UE decodes these transmit power control commands, which may be represented as bits (e.g., where a “−1” represents a “down” or reduce power command, “1” represents an “up” or increase transmit power command, and a “0” represents a “hold” command) and adjusts the uplink transmit power accordingly.
UE power consumption is dependent on both delays in decoding transmit power control commands and accuracy of decoding transmit power control commands. Long decoding delays (e.g., several subframes) may result in an undesirable amount of power consumption at the UE. Such decoding delays may be a result of using Binary Phase-Shift Keying (BPSK) modulation to decode transmit power control commands. As such, it is desirable to provide power savings at the UE. It is also desirable to reduce decoding delays while maintaining, or improving, decoding accuracy at the UE.